The gut – eye axis: can our intestines influence our eye health?

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Over the last 10-15 years there has been increasing interest in and evidence relating to the relationships between the bacteria that colonise our bodies, and our general health.

Research has begun to suggest links between the state of our microbiota (the term used to describe these colonies of bacteria living in and on us) and specific diseases and conditions, such as obesity1, depression2, type 1 diabetes3, type 2 diabetes4 and inflammatory bowel disease5. Such studies have found that people with these conditions have lower diversity in their microbiotas.

You may well have seen news stories about faecal transplants6 being used to treat persistent Clostridium difficile infections – this is now routine practice around the world in response to persistent Clostridium difficile infections. Gut microbes have also been found to play roles in mediating tumour growth, immune system functions, metabolic efficiency and a range of neurological and developmental health issues as well.

At present we know far less than we need to know. But the emerging evidence points to far more complex links between the health of our guts and that of our eyes. What we eat may affect our eye health in far more subtle and intricate ways than we previously thought. ARVO 2019 provided a session dedicated to the research in this area, so vision and eye health researchers and clinician scientists are beginning to pay serious attention to the possibility that gut health may = healthy eyes?

the emerging evidence points to far more complex links between the health of our guts and that of our eyes

What does the health of the bacterial colonies in our bodies have to do with the health of our eyes? Migration of microbes7 from one part of the body to another area or areas, whether due to leaky intestinal membranes, or other circulatory / lymphatic routes, has been found to occur far more often than previously thought. However, received wisdom has been that the eyes are immune privileged in some interesting and unusual ways, so surely this would protect them from the transmigration of microbes?

Apparently not, as research in mice has found that autoimmune uveitis can be caused by T cells (a type of lymphocyte which develops in the thymus that plays a central role in the immune response) that have been activated by gut bacteria8 to target retinal proteins. Once activated these T cells travel through the circulatory system to the eye, where they cause the autoimmune response leading to uveitis. Other research9 has shown that the surface of our eyes has its own bacterial ecosystem, requiring further investigation.

It seems likely that we will see more research in the areas of the ocular microbial ecosystem, and the interactions between eye health our microbial flora and fauna systemically.

Michael Bowen is Director of Research at the College of Optometrists, where he has developed the College's Research Strategy over the past ten years. Michael's academic background is in psychology, biology and medical ethics. Prior to his role at the College Michael worked for the professional and regulatory body for Psychotherapy in the UK.

Michael has developed and carried out research in a number of areas, and was the Lead Investigator for the PrOVIDe project, a multi-site study to gather data on the prevalence of visual impairment among people living with dementia and to explore the experiences of eye health provision of people living with dementia. their family and professional carers and eye health professionals. PrOVIDe was a collaboration between the College, Alzheimer's Society UK, The Thomas Pocklington Trust and academic partners from City University London, University College, London, Birmingham University, and Newcastle University. Michael recently worked with UK leaders in the fields of computer science, image analysis and eye health to deliver a Royal Society Science+ event entitled ‘The transformative potential of data and image analysis for eye care’.